How have the courts interpreted the doctrine of exhaustion of state remedies in the context of federal habeas corpus?

It has been said that the courts have not "always followed an unwavering line in their conclusions as to the availability of the Great Writ and that development of the law of federal habeas corpus has been attended, seemingly, with some backing and filling." Fay v. Noia, 372 U.S. at 411-12, 83 S.Ct. at 834. No area presents that picture more clearly than the issue posed by the "new facts" aspect of the doctrine of exhaustion of state remedies.²³ Nonetheless, certain general principles emerge.